Watching a new species evolve

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A new hybrid species of bird has evolved in the Galapagos Islands, after a male of one species mated with a female of another species.

On the 15th of September 1835, Charles Darwin set foot on the Galapagos Islands. This was part of his five-year voyage around the world, which helped him develop his theory of evolution by natural selection. On the Galapagos Islands, he found several unique bird species which all resembled one mainland species, but which were slightly different from each other. These birds, now called “Darwin’s finches” helped him understand how one original species could evolve into several new species.

Over 150 years later, in 1981, Professors Peter and Rosemary Grant were carrying out research on Daphne Major, one of the Galapagos Islands. They set up “mist nets” in order to capture and study the populations of Darwin’s Finches on the island. One of the birds they caught was completely different from the others on the island. This male bird was much larger and had its own unique song. They knew the bird must have come from one of the other islands, but they didn’t know where, or what species it was. The bird mated with one of the female birds on the island, and over the last 36 years the researchers and their team have kept track of the bird and its offspring, and have created a family tree using DNA samples. With all of this information, the researchers have now shown that a new hybrid species has formed. The work was published in the journal Science.

Normally, when two species of animal mate, the offspring produced are infertile. For example, a donkey and a horse can mate to produce a mule, but two mules cannot mate to produce more mules. But occasionally hybrid offspring are fertile and can mate with other hybrids to form their own species. Although there are a few animal species that we know evolved by this process, it has never been directly observed – until now.

Using genetic analysis, the researchers identified the original immigrant male as a large cactus finch. It had managed to fly all the way from the island of Espanola to Daphne Major – a distance of over 100km. It mated with a medium ground finch female on Daphne Major to produce four sons and one daughter. These then mated with each other, and have given rise to several generations. This new species has been called “Big Bird”.

“It has a unique morphology,” explain Peter and Rosemary. “In body size, and size and shape of the beak, it differs from the four other species on the island. It eats a variety of foods and cracks seeds efficiently. Put all of these together and the Big Birds stand out as occupying a unique ecological niche.”

However, there is some uncertainty about how long this species will last.

“They are inbred, but like some other island populations of birds, they seem to be able to tolerate a moderately high level of inbreeding. There is a risk that in future the level of inbreeding will be too great and the population may indeed become extinct.”

But for the meantime, the species seems to be doing quite well. Although most species don’t evolve in this way, the Big Birds are an example of how, in some rare cases, the evolution of a new species can be rapid – taking just a few years, rather than millions of years.